Method and apparatus for production of plaster plates having 4 tapered edges

ABSTRACT

A method for producing plaster plates ( 44 ), according to which two fine cardboard-covered sheets of paper ( 8, 9 ) enclose a plaster-based hydraulic binder ( 10 ) in a shaping device ( 13 ), creating a composite band ( 45 ) that is hardened on one or several hardening bands ( 14, 15 ), the edges of said hardening bands ( 14, 15 ) being provided with two bands used for tapering in the horizontal direction.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for producingplasterboard with four tapered edges at the outer edge of each board.

The invention is in the field of continuous plasterboard production inwhich two sheets of cardboard-type paper, the lower one of which,because of its color is called the cream or facing paper (hereinafterthe facing paper) and the other upper one being called the gray orbacking paper are unrolled and come to enclose a plaster-based hydraulicbinder inside a shaping means in the form of shaping plates or shapingrollers.

These two sheets of paper constitute, with the hydraulic binder, acomposite strip which generally hardens on two hardening belts at theedges of which two narrow taper reservation strips are present allowingthe future board to be provided with longitudinal tapered edges.

This composite strip is cut to the desired length, passed through thedrying oven and is finally recut to its definitive length before beingstacked. Such a method is well-known and will not be described furtherin detail in this specification.

The value of having tapered edges all around plasterboard has been knownand appreciated for many years. Indeed, they facilitate the abutment andjointing of plasterboard and allow large surface area constructions tobe built with excellent flatness characteristics and mechanicalstrength.

For many years now, it is known how to produce plasterboard with taperedlongitudinal edges on continuous manufacturing lines but there is nomethod allowing production, on such continuous operating lines, ofplasterboard with transverse tapered edges having the samecharacteristics as the longitudinal tapered edges.

There have obviously been numerous attempts and numerous patents havebeen taken out, essentially US patents, attempting to resolve thisproblem of continuous production of tapered transverse edges. U.S. Pat.No. 2,238,017 in particular attempted, in 1941, to create excessthickness by bending of cardboard but this invention never went intoindustrial development probably because the bending did not withstandthe tension in the paper or the weight of the hydraulic binder. U.S.Pat. No. 2,991,825 attempted, 20 years later, to make imprints in ashaping roller system but this was not followed up by Industrialdevelopment certainly because the imprint generated got wiped out bycrushing on the hardening belt.

It must be recognized that currently, plasterboard with taperedtransverse edges if boards do exist are either the result of machiningof the edges called tapering or feathering or artifices such asgrooving, pressing and bonding of the edge, or, more frequently, areprovided by the artisan who simply planes the edge of the board toprovide a transverse taper.

The solutions are all expensive and impact on the production cost of theboard with, additionally, the taper being far from having the qualitiesof the longitudinal taper. There is currently a real need on the marketand a real call from the industry regarding this situation.

SUMMARY OF THE INVENTION

The method and apparatus according to the invention allow thesedisadvantages to be overcome.

A solution to the problem posed is, according to this present invention,in a production line of the type discussed above, a method consistingin:

-   -   continuously preparing expandable, flexible, lightweight spacers        or packing pieces,    -   cutting said packing pieces to a length equal to a width of the        plasterboard being produced less a value comprised between 0 and        10 cm,    -   applying adhesive to an upper face of said packing pieces,    -   continuously bonding said packing pieces on-the-fly to the        bottom of one of said cardboard-type paper sheets transversely        thereto, centered, and perpendicular to a direction of        advancement of said paper sheet at accurate regular intervals        “p”,    -   bonding said packing pieces to said paper sheet in a region        ahead of said shaping means,    -   allowing said packing pieces to be carried along by said paper        sheet,    -   adjusting a tension in said paper sheet so as to regulate a        width of an imprint created therein,    -   leaving said packing pieces fastened to said paper sheet for the        time needed to pass through said shaping means and the time        needed for the composite strip composed of said paper sheets and        the hydraulic binder to harden,    -   cutting the composite strip with knife means in the middle of        the imprints left by said packing pieces.

The result is a new method and apparatus for production whichcorresponds well to the requirements of the problem posed, thetransverse taper resulting from the imprints having surface, appearance,and strength characteristics identical to those of the longitudinaltaper and been produced using a continuous process which has proved tobe very low cost and useful for industrialists and the plasterboardmarket.

The description and drawings below show one example of the production ofplaster-based paper-faced board showing the particular advantages of theinvention like those mentioned above, but have no limiting character:other production is possible in the framework of the scope of theinvention, in particular the production of plasterboard using inorganicmaterial-based papers or glass mat in place of paper or cardboard or yetagain, more generally, production of board using two sheets or a casingregardless of its nature, enclosing, after passage through a shapingmeans, a hydraulic binder that sets or dries.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a shows the production line head in which the new method of theinvention is implemented.

FIG. 1 b shows a board with four tapered edges produced according to theinvention.

FIG. 2 shows the apparatus according to the invention for preparing,positioning and bonding packing pieces or spacers on the facing paper.

FIG. 3 is a view in the direction of arrow F of the apparatus in FIG. 2.

FIG. 4 is an alternative embodiment of the apparatus according to theinvention for preparing, positioning and bonding the packing pieces ontothe facing paper.

FIG. 5 is a view in the direction of arrow F of the apparatus in FIG. 4.

FIG. 6 shows the device of the invention for unbonding the packingpieces and cutting the composite strip.

FIG. 7 shows the packing piece bonded below the facing paper accordingto the invention.

FIG. 8 shows the bonded packing piece of FIG. 7 after going through theshaping means of the invention.

FIG. 9 shows, according to the invention, a first alternative embodimentof a packing piece bonded below the facing paper.

FIG. 10 shows the packing piece as bonded in FIG. 9, after passingthrough the shaping means.

FIG. 11 shows a second alternative embodiment of a packing piece bondedbelow the facing paper.

FIG. 12 shows the bonded packing piece of FIG. 11 after passing throughthe shaping means.

FIG. 13 shows a third alternative embodiment of a bonded packing piecebelow the facing paper.

FIG. 14 shows the bonded packing piece of FIG. 13 after passing throughthe shaping means.

FIG. 15 shows a fourth alternative embodiment of packing piece 5.

FIG. 16 shows a fifth embodiment of a packing piece bonded below thefacing paper.

FIG. 17 shows the bonded packing piece of FIG. 16 after passing throughthe shaping means.

FIG. 18 shows a sixth alternative embodiment of bonded packing piecebelow the facing paper.

FIG. 19 shows the bonded packing piece of FIG. 18 after passing throughthe shaping means.

FIG. 20 shows a bottom view of the facing paper after bonding thepacking piece and stamping said paper according to the invention.

FIG. 21 shows a seventh alternative embodiment of bonded packing piecebelow the facing paper.

FIG. 22 shows the bonded packing piece of FIG. 21 after passing throughthe shaping means.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The method of the invention consists, firstly, in the continuouspreparation at a high production rate of the packing pieces or spacers5. These packing pieces 5 come from an inexpensive, lightweight flexibleexpandable material; they are between 1 and 2 mm thick and between 5 and20 mm wide with their length being equal to the width of the board inthe process of production less a value of between 0 and 10 cm.

These packing pieces 5 are removed from a roll 26 of flexible strip 27,cut to length and carrying a layer of adhesive on their upper face.

In one embodiment of the method, the packing pieces 5 are of a materialhaving the same expansion when moist as the facing paper 8 to which theyare fastened. They can for example be a packing piece of paper of thesame nature as the facing paper 8, so that the composite strip 45 canexpand freely without being retained by the packing piece 5 whilehardening.

According to an embodiment of the method, the packing pieces 5 aresubjected to a certain number of machining operations to improve theiruseability such as:

-   -   a shaped or tapering cut at the ends of the packing piece 5 to        control the future shaping of the ends of the tapered transverse        edge 17.    -   a thinning down of the ends to also improve the future shaping        of the ends of the transverse taper 17.    -   flattening or rounding of the sharp edge of the flexible strip        27 to give a rounded packing piece 51 which is less likely to        get caught up during its future movement within the mixer 1 and        shaping means 13 region.

The method of the invention next consists in bonding the packing pieces5 underneath the facing paper 8 in a region which of necessity is priorto the shaping means 13, meaning that it can be between the mixer 1 andthe shaping means 13 or yet again, between the mixer 1 and the roll offacing paper 8 and is, according to the invention preferably just infront of the mixer 1.

The bonding of the previously prepared packing pieces 5 below the facingpaper 8 is, according to the method of the invention, an operation whichis done on-the-fly, continuously, and at high frequency. The packingpieces 5 are positioned perfectly centered and quite perpendicular tothe direction of advancement of the facing paper 8.

They are fastened to the facing paper 8 at intervals between themcalculated, taking account of the longitudinal expansion of thecomposite strip 45 while it is setting, so as to correspond to theexpected final length of the plasterboard 44 after it has dried allowingfor the excess length necessary for sawing the plasterboard 44 when itleaves the production line, such calculation being well known to thoseskilled in the art.

The landing means implemented for bonding the packing pieces 5on-the-fly are arranged so that the facing paper 8 undergoes nodeviation nor deformation which could be prejudicial to the correctmanufacture of the plasterboard 44.

According to the invention, one method adopted for bonding the packingpieces 5 is adhesive bonding, the bonding parameters being controlled toensure the packing piece 5 fastened to the facing paper 8 by adhesivebonding does not interfere with the expansion thereof perpendicular tothis bonding. The parameters that are adjusted are the following:

-   -   the choice of adhesive bonding by dipping or spraying,    -   the amount of adhesive 24 deposited and the distribution of the        adhesive 24 over the packing piece 5,    -   the discontinuity or continuity of the adhesive film 24 over the        packing piece 5,    -   the elasticity and tack characteristics of the adhesive 24.

In one embodiment, the means used for introducing and bonding thepacking pieces 5 on-the-fly additionally serve to roughen the facingpaper 8 at both sides of a packing piece 5; this can be done bystamping, knurling, pricking, brushing and so on. Thus, the regioncorresponding to the future transverse tapering 17 will be better keyedto the jointing product, and the mechanical strength of the connectionbetween plasterboard elements 44 will then be greatly improved.

In one embodiment, the means used for bonding the packing pieces 5on-the-fly also serve to pre-mark the facing paper 8 with two notchlines 11 parallel to packing piece 5 and at a distance of between 5 and9 cm from the axis of the packing piece 5. Pre-marking of the facingpaper 8 in a region which will later constitute the beginning of thetransverse tapering 17 will improve the configuration and appearance,these notch lines 11 delimiting the rough surface 12.

The method then consists in protecting the packing pieces 5 carried onthe facing paper 8 against accidentally being torn off through theaction of mechanical parts present between the mixer 1 and the shapingmeans 13, and for this, in this region, all the points of engagement andall projecting points 19 are removed or rounded off.

According to an embodiment, to facilitate the passage of the packingpieces 5 through the region between the mixer and shaping means 13, aflexible, slippery and wear-resistant guide sheet 42 is placed betweenthe mixer 1 and the entry to the shaping means 13, this guide sheet 42,which is wider than the length of packing pieces 5, is secured at itsupstream end by securing means 47 and it is then left free, this guidesheet 42 covering all the tooling means present in the region such asthe table 48, the beaters 18, the facing paper guides 8, withoutinterfering with their effectiveness. The guide sheet 42 ensures perfectsliding of the packing pieces 5 so they cross the region between themixer 1 and shaping means 13.

The method then consists in allowing the packing pieces 5 to firstlypass through the shaping means 13 but also in waiting for a period oftime sufficient for the composite strip 45 to harden so that the imprint20 left by the packing pieces 5 at the facing paper side 8 of compositestrip 45 is permanent and definitive.

The method then consists in stripping off the packing pieces 5on-the-fly and discharging them to waste 43, unbending being able to bedone at any point where the above-mentioned hardening time issufficient. This is preferably the region 23 between the two hardeningbelts 14 and 15 or just ahead of the shear 2.

Stripping off consists in removing the packing piece 5 with a brush 22which, after removing a packing piece 5, is retracted so as to notinterfere with the facing paper surface 8. This brush 22 is inclinedwith respect to the line so that brush 22 is more effective in breakingthe bond of the packing piece 5. Removal is all the more easy as, thefacing paper 8 at this stage in the method, becoming moist, littleenergy is required to remove the packing piece 5.

According to an alternative embodiment of the method, the packing pieces5 are removed using jets of compressed air or yet again by burning thepacking piece 5 with suitable burners.

According to another alternative embodiment, the packing pieces 5 arenot removed and then remain bonded to the composite strip 45, their lowmechanical strength allowing them to be readily cut by a single knifestroke at right angles thereto, said packing pieces 5 then continuingtheir circuit to be destroyed by sawing at the end of the plasterboardline. Nevertheless, the method provides for weakening of the packingpiece 5 at its main axis. For this, it can be the flexible strip 27which is appropriately designed or it can also be a tool which weakensthe flexible strip 27 along its main axis while the packing pieces 5 arebeing prepared.

The last stage in the method consists in cutting the composite strip 45with a knife or shear 2 at the imprints 20 left by packing pieces 5. Theimprints 20 are between 10 and 18 cm wide, in other words several timesgreater than the width of packing piece 5.

The result, at this stage in the method is a plasterboard element 44with four tapered edges at its periphery, the two longitudinal ones 16being conventional and the transverse ones 17 having been created by themethod of the invention. The plasterboard 44 then passes through thedrier, is sawn to length and then stacked to be stored.

According to an embodiment, the knife or shear 2 stroke takes placesimultaneously in the imprints 20 and at a distance equal to that of twoimprints 20, the board elements 44 thus produced having three taperededges, two longitudinal ones 16 and a single transverse one 17. Suchboard elements with three tapered edges are useful for some particularapplications in the market.

According to the invention, the exact shape and dimensions of thepacking piece 5, the notch lines 11, the packing piece end shapingoperations discussed above and of the adjustment of the tension in thefacing paper 8 allow the shape of the imprint 20 to be controlled alongwith its width of between 10 and 18 cm; indeed, these parameters allinfluence the shape and dimension of the imprint 20 left by the packingpiece 5.

According to one alternative embodiment, the packing pieces 5 arereduced to a single wire or even 2 wires of some few mm² cross section.The wires are circular or square, the usefulness of the wire being thatit is readily put into a roll and his very inexpensive, so the methodhas available to it single wire packing pieces 52 and double wirepacking pieces 55.

According to one alternative embodiment, the packing pieces 5 areextracted from a flexible strip 27 still between 5 and 20 mm wide butwith a thickness reduced to a few tenths of a mm thus being moreeconomical and advantageous for the method. To artificially increase thethickness of the packing piece 5 cut in the flexible strip 27 which isquite thin, this increase in thickness being necessary for the method ofthe invention, small holes are pricked in it over its length by at leastone row of pins. The pricking operation 58 locally raises the materialof the flexible strip 27, pushing it up, see reference 59, and therebyartificially increasing the thickness of the flexible strip 27 and thismethod gives a pricked packing piece 57 which is highly economical. Inone embodiment, the pricked packing piece 57 is pricked over one orseveral lengths. According to another embodiment, the ends of thepricked packing piece 57 are pricked with a chosen depth andprogressiveness, thereby having better control of the shaping of theregion of intersection between the transverse tapering 17 and thelongitudinal one 16.

In the method, the packing pieces 5 are made from one of the followingmaterials, paper, plastic material, organic material, metal, orcomposite material.

According to one alternative embodiment, the packing piece 5 takes theform of one or two heat-bonded plastic wires. The advantage here is thatof having a material that avoids the stage of adhesive bonding thepacking piece 5, being as it were a two-in-one packing piece 56.

In one alternative embodiment, the packing pieces 5 come from a readilyconsumable material such as paper, so that they can be burnt prior toshearing 2, to remove them from composite strip 45; the other advantageof this embodiment is that it avoids having to get rid of the packingpieces after use.

In another alternative embodiment, the packing pieces 5 come from a roll26 of self-adhesive tape which has the advantage of good regularity ofbonding of the packing piece 5 to the facing paper 8 allowing theadhesive applying means 30 or 60 to be dispensed with.

According to yet a further embodiment, advantage is taken of contactingthe facing paper 8 either with a linearly moving bonding follower 6 or arotary bonding follower 7 for marking the transverse tapers with an inkjet printing system. Thus, this new transverse tapering 17 can behighlighted and made more evident.

The linearly moving bonding follower 6 associated with the method of theinvention shown inside the dash-dot line rectangle 3 of FIG. 1 a detailsof which are given in FIGS. 2 and 3, proceeds with all steps frompreparation of the packing pieces 5 right up to their bonding below thefacing paper 8.

At the beginning of the process, we find a roll 26 of flexible strip 27of about 1.5 by 10 mm section. This roll 26, which is driven andtransported by small rollers 28 engages flexible strip 27 on lower table29 perpendicularly to the direction of unwinding of the facing paper 8,said lower table 29 being underneath and at a certain distance from thefacing paper 8. The flexible strip 27 is covered while it moves towardslower table 29 with a very thin film of adhesive 24 by the adhesiveapplying means 30, this flexible strip 27 then being cut to length byknife 31 to become a packing piece 5. This packing piece 5 isconsequently positioned perpendicularly to the direction of unwinding ofthe facing paper 8 at a distance from and below the latter, and centeredwith respect thereto by the small rollers 28 and their associatedposition detector.

The lower table 29 which is part of the linearly moving bonding follower6 is set in motion at the same speed as facing paper 8 by means ofcarriage 70, said carriage 70 being driven by drive transmission means33 associated with an electronic system and pulse sensor 32. The pulsesensor 32 which is stationary with respect to the linearly movingbonding follower 6 is permanently aware of the position of the packingpieces 5 with respect to facing paper 8. Lower table 29 is now movingwith the same speed as facing paper 8 and at this very precise moment,lower table 29 performs an up-and-down movement on jacking and guidemeans 34, compressing and bonding the packing piece 5 beneath the facingpaper 8, said facing paper 8 then being supported by abutment againstcompressible abutment plate 36 itself fixed to the upper counter-table36. Packing piece 5 thus fastened on-the-fly is carried along by thefacing paper 8 without having modified or disturbed the movementthereof. The linearly moving bonding follower 6 at position “P2” duringbonding of the packing piece 5 now returns to its starting position“P1”. A new positioning and bonding of packing piece 5 cycle starts,with a new packing piece 5 being bonded while respecting a preciseinterval “P” with respect to the preceding packing piece 5, and thus thecycle repeats over again.

This interval “P” depends on the length of plasterboard element 44required, on the longitudinal expansion of composite strip 45 while itis hardening on the hardening belts, and on the excess length necessaryfor sawing plasterboard elements 44 at the end of the line. This gap isreadily calculated by the person skilled in the art and is adhered tousing pulse counter 32, suitable electronics and drive and transmissionmeans 33.

According to one embodiment, the sharp edges of packing pieces 5 arerounded off, their ends are chamfered and tapered. This is performed bytool means in line with the adhesive applying means 30 and the shear orknife 31, responsible for machining the flexible strip 27 at the time ofits passage and engagement on lower table 29.

In one embodiment, a rough surface 12 and two notch lines 11 are createdat each side of a packing piece 5. FIG. 20 shows more detail of how thisrough surface 12 and notch lines 11 of facing paper 8 at each side of apacking piece 5 appear. The tool associated with this embodimentconsists of a stamper 37 and counter-stamper 38 fixed to the uppercounter-table 35 which, when the lower table 29 moves upwards, slightlystamps and consequently embosses, the facing paper 8.

In one embodiment, the flexible strip 27 a few tenths of a mm thick usedfor producing packing piece 5 is pricked along one or several lines inits longitudinal sense. The tool used here is in line with the adhesiveapplying means 30 and shear or knife 31. This tool has means foradjusting the depth of pricking. The adjustment allows regulation of theoverall thickness or apparent thickness of the flexible strip 27 andconsequently of the depth of the transverse tapering 27 being sought.The two ends of the packing piece 5 are pricked more strongly andprogressively, to improve the profile of the point where a horizontaltapering 16 and transverse tapering 17 meet.

In one embodiment, a rotary bonding follower 7 performs, just like thelinearly moving bonding follower 6, the functions of preparing,positioning and bonding at a precise interval of the packing pieces 5below the facing paper 8. FIGS. 4 and 5 show this rotary bondingfollower device 7, and on FIGS. 4 and 5, there can be seen the lowerroller 40 and upper roller 41, and the same pieces of apparatus will beseen on this rotary bonding follower 7 as those already seen on thelinearly moving bonding follower 6, in other words: the roller 66,flexible strip 63, small roller 71, adhesive applying means 60, shearron knife 61, pulse sensor 69, jacking means and guides 64, compressibleabutment plate 65, stamper 67 and counter-stamper 68.

The preparation and positioning of the packing pieces 5 on the lowerroller 40 is done similarly to the preparation of the packing pieces 5on the linearly moving bonding follower 6. The rounding of the sharpedges of the packing pieces 5, their chamfering and end tapering is alsodone in analogous fashion to that used for packing piece preparation onthe linearly moving bonding follower 6.

The essential difference between this rotary bonding follower 7 and thelinearly moving bonding follower 6 resides in the manner of approach tothe facing paper 8, the bonding of the packing piece 5, and the stampingof the facing paper 8. These are described below.

A packing piece 5 is prepared, it is below facing paper 8 and spacedtherefrom, and makes a rear angle 46 with the facing paper 8.

By means of pulse sensor 32, and suitable electronics, lower roller 40and upper roller 41 driven by motor and transmission means 39 adopt thesame peripheral speed as the horizontal speed of the facing paper 8during angular movement equal to the rear angle 46, at the preciseinstant where packing piece 5 and compressible abutment plate 65 are inthe position shown in FIG. 4, the jacking means and guides 64 receive acommand to lower and raise the upper roller 41 thereby bonding thepacking piece 5 underneath the facing paper 8. The packing piece 5, thusbonded on-the-fly, is carried along by the facing paper 8 without havingmodified or disturbed the movement of the facing paper 8.

The upper 40 and lower 41 rollers then move back at angle 46 and a newpreparation, positioning and bonding cycle starts, a new packing piece 5being bonded while respecting a precise interval “P” with the precedingpacking piece 5, and the cycle repeats over again in this way.

How this interval “P” is calculated was explained above. This issomething the skilled person is perfectly able to calculate and which isadhered to in practice by pulse sensor 69, suitable electronics andmotor and transmission means 39.

At the moment of bonding, stamper 67 and counter-stamper 68 slightlyemboss the facing paper 8 to obtain a rough surface 12 and the two notchlines 11, as discussed above: the rough surface will coincide with thetransverse tapering 17 and the notch lines 11 will coincide with theline where the transverse tapering 17 starts.

One embodiment of the device involves facilitating the passage of thepacking pieces 5 and their sliding within the region between the mixer 1and shaper 13. This involves the use of a flexible guide sheet 42 whichis slippery and wear resistant, this latter wear resistancecharacteristic being essential as the guide sheet 42 will have thefacing paper 8 and all packing pieces 5 passing over it. Said guidesheet 42, which is wider than the length of the packing pieces 5, isheld by fasting means 47 upstream of the mixer 1 and shaping means 13region, and is centered with respect to the movement of the facing paper8 and consequently the packing pieces 5, the guide sheet covering allthe areas of friction and possible snagging in the region between mixer1 and the start of shaping means 13.

This guide sheet 42 covers the table 48, the beaters 18, projectingpoints 19, guides for the facing paper 8 and thus protects the packingpieces against any risk of becoming detached in this region.

Last, means are provided for stripping off the packing pieces 52 todischarge them to waste 43. This is a brush 22 which rotates permanentlyand which is inclined with respect to the line. This brush is operatedby the jacking means 25 which raise the brush 22 only when packingpieces 5 are passing. The jacking means 25 are controlled by thedetector for imprints 21 and its associated electronic system whichcalculates the point in time at which the jack should be raiseddepending on the distance d1 between the imprint detector 21 and thebrush 22, and the speed “V” at which the composite strip 45 is moving.

The stroke of the shear or knife 2 in alignment with imprint 20 left bypacking piece 5 is controlled by imprint detector 21 and associatedelectronics which take account firstly of a distance d2 between imprintdetector 21 and shear or knife 2, and, secondly, the speed “V” at whichthe composite strip 45 is moving.

1. A method for continuous production of plasterboard elements in which two cardboard-type paper sheets enclose, within shaping means, a plaster-based hydraulic binder to create a composite strip which then hardens on two hardening belts carrying at their edges two tapered strips for producing longitudinal tapered edges thereon, comprising: continuously preparing flexible, lightweight spacers or packing pieces between 1 and 2 mm thick and 5 to 20 mm wide, cutting said packing pieces to a length equal to a width of the plasterboard being produced less a value comprised between 0 and 10 cm, applying adhesive to an upper face of said packing pieces, continuously bonding said packing pieces on-the-fly to the bottom of one of said cardboard-type paper sheets transversely thereto, centered, and perpendicular to a direction of advancement of said paper sheet at accurate regular intervals, wherein during said bonding step, said packing pieces are bonded to said paper sheet in a region ahead of said shaping means, allowing said packing pieces to be carried along by said paper sheet, adjusting a tension in said paper sheet so as to regulate a width of an imprint created therein by the packing pieces to between 10 and 18 cm, leaving said packing pieces fastened to said paper sheet for the time needed to pass through said shaping means and the time needed for the composite strip composed of said paper sheets and the hydraulic binder to harden, and cutting the composite strip with knife means in the middle of the imprints left by said packing pieces.
 2. The method according to claim 1, wherein said packing pieces are stripped off on-the-fly after said composite strip has hardened in a region extending from an end of a hardening belt to said knife means, and preferably in a region located between hardening belts immediately following one hardening belt, or in a region located close to and ahead of said knife means.
 3. The method according to claim 1, wherein said packing pieces are cut from a roll of flexible strip which is of paper, plastic material, organic material, metal or composite material.
 4. The method according to claim 3, wherein a pricked packing piece taken from a roll of flexible strip is pricked over its length along at least one line of pins of variable length allowing control of the overall thickness of a pricked packing piece and consequently of the depth of the transverse tapering being sought, the ends of a pricked packing piece being themselves pricked to a depth different to said height of said pins at a mid-point of said pricked packing piece.
 5. The method according to claim 1, wherein said packing piece is reduced to a wire packing piece or a double wire packing piece, said wire originating from a roll of flexible wire either of paper, plastic material, synthetic material, organic material, composite material, or metal.
 6. The method according to claim 1, wherein a surface of said paper sheet on the same side as said packing piece and at both sides of said packing piece and in coincidence with a future transverse tapering created by said packing piece is roughened either by stamping, pricking, knurling, brushing, said surface being additionally pre-marked along two notch lines parallel to said packing piece in a region corresponding to at future beginning of a said transverse taper created by said packing piece.
 7. Apparatus for carrying out a method in which two sheets of cardboard-type paper are unwound and come to enclose a plaster-based hydraulic binder in shaping means to constitute a composite strip which hardens on two hardening belts fitted with tapered strips for creating horizontal tapers in a plasterboard production line in which the apparatus further comprises: a bonder follower device located in a region ahead of said shaping means provided for preparing said packing pieces from a roll of flexible strip, for coming into contact at high frequency with one of said paper sheets for accurately bonding on-the-fly said packing pieces to the bottom of said paper sheet for roughening and pre-marking said paper sheet at both sides of a packing piece bonded to the bottom of the one said paper sheet, a guide sheet located between said binder follower device and said shaping means provided to protect said packing pieces against being torn off, and for facilitating the passage and sliding of said packing pieces between said bonder follower device and said shaping means, packing piece removing means located after a hardening belt and ahead of cutting means provided for removing on-the-fly packing pieces bonded to the bottom of said composite strip, and cutting means located after a said hardening belt and after said packing piece removing means provided for cutting said composite strip in alignment with each of a number of imprints created by said packing pieces.
 8. The apparatus according to claim 7, wherein the bonding follower device is a linearly moving bonding follower device constituted by a lower table located underneath one of said paper sheets and another counter-table situated above the said one of said paper sheets, said lower table receiving packing pieces originating from a roll of flexible strip and carrying adhesive applied by adhesive-applying means and cut to length by a knife and being provided with a stamper and jacking means and guides, said upper counter-table being fitted with a compressible abutment plate, and a counter-stamper, the two said tables being carried by a carriage moved by motor and transmission means.
 9. The apparatus according to claim 7, wherein said bonding follower device is a rotary bonding follower device constituted by a lower roller located below said one paper sheet and an upper roller located above said one paper sheet, said lower roller receiving packing pieces originating from a roll of flexible strip and carrying adhesive applied by adhesive applying means and cut to length by a knife and being equipped at its periphery by a stamper, said upper roller located above said one paper sheet in parallel with said first lower roller being equipped at its periphery with a compressible abutment plate and a counter-stamper and being connected to jacking means and guides, the two said rollers being provided with motor and transmission means.
 10. The apparatus according to claim 7, wherein a guide sheet thereof is constituted by a flexible, slippery and wear-resistant film, secured upstream of a table by fixing means, said flexible film, of greater width than a length of said packing pieces simultaneously embracing said table, beaters, projecting points, and guides for said one of said paper sheets in the region between a mixer and shaping means, said flexible film presenting to said packing pieces within said region a surface that is smooth, slippery and devoid of points where catching or snagging can occur.
 11. The apparatus according to claim 7, wherein said means for removing packing pieces consists of jacking means controlled by an imprint detector and associated electronics, said jacking means being connected to a brush itself fitted with a motor, said brush being located below said composite strip and positioned so as to be inclined with respect thereto.
 12. The apparatus according to claim 7, wherein said cutting means consist of a shear, an imprint detector at a known distance from said shear and shear stroke calculating means. 